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A large number of processes to achieve high precision laser range finder program

0fc, technical value of N that the phase difference directly, when the accuracy of 1o. If so fm = 3600fc, accuracy of 0.1o. Third, the project achieved a laser range finder. DDS implementation of the laser modulation measurements using multi-scale and frequency is to use an indirect way of measuring tape and measure the phase difference frequency technology,[link widoczny dla zalogowanych], which requires the system must have a high frequency generating device, to achieve a variety of high-speed frequency switching. And in order to ensure accuracy, requiring high precision frequency generator. Conventional VCO frequency stability is not only slow, and the frequency accuracy is not high, the task can not do the laser modulation. Now widely used in the field of electronic engineering of the DDS (direct digital frequency synthesis) technology, is very suitable as here, the frequency modulation of the laser source. DI) S block diagram shown in Figure 4. Fr Jili reference frequency control word A silkworm a phase adder output frequency of the sine table Jr r Figure 4 for the high stability frequency reference crystal, the output signal is used to provide synchronization of various parts of DDS; DDS phase accumulator is the core of It consists of an N-bit binary word adder and an N-bit sampling clock Nepal registers, the role of the frequency control word K is a linear accumulation; sine table stores one cycle of sinusoidal signal, corresponding to different phase codes address the magnitude of the output of different codes. When the phase control word to 0,[link widoczny dla zalogowanych], amplitude control word to 1, the phase accumulator 7 a N} II__1 butterfly control the output phase sequence Xiaoshan sine table of addressing range by a series of discrete codes. Coded by the magnitude of D / A conversion by the corresponding step wave,[link widoczny dla zalogowanych], and finally smoothed by low pass filter available to the analog sine wave required. DINS output frequency is f = Kr / 2 ~, the frequency resolution is Af = F/2N. By the Nyquist sampling theorem shows that, in order to restore sinusoidal signal, each cycle to ensure that at least two sampling points, so DINS of the highest attainable output frequency r / 2. From the above analysis shows that, when the DINS the phase accumulator word length and fixed word adder phase, by changing the K, P, A DINS can effectively control the output of the analog signal frequency, phase and amplitude. Many chip companies have produced considerable DINS performance chips, such as Standford's STEL2375, the maximum operating frequency up to 1GHz, the output signal bandwidth of 400MHz, the frequency resolution for the mHz level. Can see that these fully meet the performance requirements of the laser modulation. Figure 5 Figure 5 shows a simple semiconductor laser modulation circuit. Is the DC bias voltage is modulated by the DINS sinusoidal output voltage. The circuit changes the voltage of Q into changes in the laser intensity to facilitate the realization of the laser light intensity modulation. 2. Phase measurement with FPGA implementation to simplify circuit design phase difference meter, reducing the system size and power consumption, we use FPGA (field programmable gate array) to the external circuit with a small amount of phase measurement, conversion and display functions, see Figure 6. FPGA integrated circuit phase difference measurement unit most of the features, and is achieved through software programming, with strong portability and modifiability. Which the count value computing unit (phase) into the measured distance, and the environment through the method of testing the atmosphere density, temperature and other factors were corrected. Then after latch and display decoding, and ultimately sent to the LCD display. Present highly integrated FPGA chip to implement complex combinatorial logic and sequential logic functions, and can process any programming work. We can be produced by DDS frequency of its control, so the whole system without additional microcontroller or DSP chip. * 8 Figure 6 IV Conclusion In this paper, the laser ranging programs, theoretical range accuracy up to mm order of magnitude, range up to several hundred kilometers. By using the DINS chip and FPGA can greatly reduce system size and power consumption,[link widoczny dla zalogowanych], make a portable laser range finder, can be applied to geographic mapping, weapons and equipment, aerospace and other fields. It is reported that China recently developed high-precision satellite ranging range finder, the precision can reach a few centimeters. This article gives only a preliminary plan, to make practical use of the product,[link widoczny dla zalogowanych], there are many practical engineering problems to be resolved. References [1] Jin Guofan, Li Jing town. Laser Surveying. Science Press [2] Zhang Yongrui, Liu, the Yanglin Yao, Gu Yukun. Electronic Measurement Technology. Xidian University Press [3] Chao, Liu Kaipei. CPLD-based phase measuring instrument. Electronic Technology, 2003 5 Measurement Technology 2004. No9

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